Clare's Bridge - Maintenance & Repairs

A number of Great North Road bridges were built in 1830. These stone and timber bridges are the oldest existing bridges on the mainland of Australia. Of these bridges Clares Bridge is the grandest. Built at the head of gully on a sweeping curve it was designed to strikingly display the skills of the road designers and the convict workforce that built it.

With finely detailed approach walls and a central pier this bridge proudly proclaimed this is a road as good as any in England. Time has dealt unkindly with this bridge. The original decking was soon lost, possibly in a bushfire. By the 1920s the eastern corner of the northern abutment had collapsed and the eastern corner of the southern abutment was showing distress. At some stage there was a partial reconstruction of a wall to support the eastern end of the northern abutment and a partial reconstruction of the eastern side of the southern abutment which collapsed again in the early 1990s.

In the early 1960s a high voltage power line was being built to bring power from the Hunter Valley to Western Sydney, as part of this construction a modern concrete and steel decking was built at Clares Bridge. Unfortunately the designer did not understand the stress principles of filled stone abutments and had large concrete slabs poured onto the fill behind the stone face wall. In the southern abutment the bottom section of this concrete slab was poured without any formwork using the stone wall as formwork. The steel girders that carried the decking were attached to these concrete slabs. The bridge was then used to carry the heavy construction vehicles.

In the late 1960s early 1970s several truck loads of road fill had been dumped for storage on what had been a by-pass road on the western side of the bridge. Before it could be used very heavy rain washed this road fill away and it collected as silt between the abutments. This silt hid the damage that was occurring in the centre of the southern abutment. By 1987, a serious crack appeared in the SE wall corner with the bridge abutments. In 1988, that section of the wall and the abutment collapsed.

The National Parks and Wildlife Service obtained an assessment of the damage and by early 1999 had obtained funding for repair work to be undertaken. When as part of this work the silt between the piers was excavated it was found there was a very large bulge in the central section of the southern abutment which appeared in danger of collapsing. As the NPWS only had funding for the restoration of the coroner they carried out the work they had funds for and propped the central section of the abutment. In the course of gaining approvals for this work it was realized this section of the road actually as under the management of Gosford Council.

In 2002 members of the Convict Trail Project and Gosford City Council inspected the bulge in the abutment and the Convict Trail Project with assistance from Gosford City Council successfully applied for an Environment Australia Cultural Heritage Project Program grant to complete this restoration. Below are the story and pictures of the 1999 and 2004 reconstruction of different sections of the Southern Abutment This work completes the conservation of the Southern abutment.

1999 NPWS funded work

The 1999 Restoration Work. The conjectural reconstruction of south east corner of the Southern Abutment

Following the consideration of the damage assessment which the NPWS obtained, discussions took place between Tony Horwood (NPWS), Albert Kraan (stonemason), Paul Budde and Lorraine Banks (both of CTP).

The planning of the work by Albert Kraan and the NPWS produced a result which saw Clare's Bridge restored to provide a sound structure. During the work of clearing the area ready for the wall and abutment to be restored, there were two exciting finds. It was discovered that Percy Simpson and Arnold Clare had constructed a pavement between the outer walls and the central stone pier, using large slabs of rock as cobblestones. The pavement was designed to and did prevent the structures being undermined by water flowing over them. The cobblestones had been buried in up to 1.5 metres in silt. The second event was that it had been known that there was an additional wall in the gully just downstream of the bridge. This wall was temporarily revealed, along with a number of loose blocks further downstream. Such finds have shown how much careful thought went into building a high quality bridge in the 1830s.

On Heritage Week, a visit was paid to the restored bridge by a large group of people. There was also media attention given to the work which was done, with appropriate recognition of all those involved. Who better to explain what was done than Albert Kraan, the stonemason, to the ABC News team.

The 2004 Restoration Work. The conservation of the cental section of the Southern Abutment

The Convict Trail Project applied for and obtained an Environment Australia Cultural Heritage Project Program 2001-2 Grant to conserve the central bulging section. Gosford City Council paid for the geotechnical and heritage engineering advice which found the best way of protecting the convict built abutments was to remove the 1965 decking. The geotechnical advice was provided by RCA Australia and the heritage engineer was Bill Jordan of Bill Jordan and Associates

In April 2004 Gosford City Council bridge team removed the bridge decking.

To get access to the southern side of Clares bridge the small bridge at Ten Mile Hollow had to be temporary propped to an eleven ton limit the weight of the stonemasons truck. This was done using labour from the Metropolitan Periodic Detention Centre prisoners from Silverwater, and NPWS works staff working to a plan, voluntary designed by Jim Alexander consultant bridge engineer of Gosford.

Before work commenced the area to be conserved was photographed and as each stone was removed it was numbered in wax crayon with a unique number which was recorded on the picture of the stone. This enabled each stone to be returned to exactly the same spot it came from.

With the decking removed the stonemason Ken Fletcher of Wollombi Stonemasonary Services with a crew of three started deconstructing the central section of the southern abutment. Numbers in red paint showed the top three rows of stones had been removed before, probably when the top of the abutment was excavated prior to pouring the concrete slab. The backs of the second top row of stones had been captured by the concrete and most had broken when the wall slumped.

With the top three rows of stone deconstructed the concrete slab had to be removed with out any vibration or further damage to the wall. After discussing many options it was decide to have the approximate 10 ton slab sawn into five pieces each weighting approximately 2 ton, these could be lifted by the crane on the stonemasons truck.

With the concrete slab cut, the stonemason and crew retuned, setting up camp at Ten Mile Hollow. Staying here in mid winter during the week for the six weeks it took to complete the work.

The bulged central portion of the southern abutment was carefully deconstructed. During the deconstruction a number of stones were found to be broken parallel to the face and had to be repaired or replaced. One of these stone was a corbel stone. As it is hoped to replace the decking this stone had to repaired in a way that the suspended section of the corbel could be load bearing. This was done by the use of Cintec Anchors. These were kindly donated by Cintec Australasia Pty Ltd and the installation of same donated by Greg Searles of Concrete Peripherals. The second bottom row of stone was found to be badly crushed and mostly had to be replaced. There were a number of original stones left from the 1999 reconstruction sometimes with broken corners etc. Most of the replacement stones were recut from these stones. Only 4 new stones were introduced into the reconstruction.

With all the additional work, the project was running badly over budget. TransGrid the descendant of the Electricity Commission was asked to assist, this they generously did. This funding allowed a small section in the top of the abutment that had not been completed in 1999 to be completed. Six new stones were be used in this small section.

In history Week 2004 a large group of people visited the bridge to see the new work. It is hoped in the near future to be able to replace the decking on Clares Bridge. It is planned that this new decking will be sympathetic to the original decking.

The archaeological evidence of the corbel stones, plans for a similar bridge in Tasmania and bridge design text books tell us about the probable style of decking that was on this bridge but despite extensive searching so far the original plans have not been found. We know the timber would have been cut from appropriate nearby trees so species lists and the present of current trees give us the timber types but again no records have been found of timber types or sizes. The roads department was reorganised in 1830 and it is believed these records were lost in this reorganisation.Clares Bridge can be visited any time by walking or by bicycle. Occasionally both the Convict Trail Project and the NPWS conduct two and four wheel drive tours to Clares Bridge.